1. Field of the Invention
This invention relates to novel polymeric gel compositions, useful in temperature-indicating devices, containing a polydiacetylene and a gel-forming liquid therefor, and also to a novel class of polydiacetylenes, useful in forming the gel compositions, formed from monomeric diacetylene diol-bis(alkoxycarbonylmethylurethanes).
2. Brief Description of the Prior Art
Two types of clinical thermometers currently on the market utilize organic compounds as temperature indicating materials in which a color change occurs at a predetermined temperature. Both types of devices are based on particular phase changes of organic compounds, or mixtures thereof, as the principle underlying the color change.
The first type of device (developed by Bio-Medical Sciences Inc., Fairfield, N.J.) uses the principle of the melting of organic compounds, in which the melt carries a co-mingled dyestuff through a white or colorless absorbing material, so as to produce a visual color change. However, the device in general is not reusable and also requires a protective film between the melting compositions and the dyestuff, and in some cases storage at low temperatures prior to use; factors which tend to increase the overall manufacturing cost. Various modifications of the device are described in the following patents assigned to Bio-Medical Sciences Inc.: U.S. Pat. Nos. 3,981,683 (1976); 3,665,770 (1972); 3,677,088 (1972); 3,704,985 (1972); 3,966,414 (1976); and 3,980,581 (1976).
A further device is described in U.S. Pat. No. 4,042,336 (1977), assigned to Bio-Medical Sciences, Inc., in which the temperature history of a product is visually displayed as a color front on an indicator, initiated by a generated gas, the distance of the front advancement being a function of the temperature-time integral.
The second type of device (marketed by Clinitemp, Inc., Indianapolis, Ind.) uses color changes produced by liquid crystal transitions, as viewed through either a polarizing or a colored film. These liquid crystal devices are reversible and thus reusable but have no hysteresis associated with the color change. As a result, there is little time to record the temperature once the device is detached from the skin or removed, for example, from the mouth.
U.S. Pat. No. 3,479,877 (1968) discloses a temperature indicator device wherein an indicator substance melts, at a predetermined temperature to be monitored, and flows along a wick, the distance of flow corresponding to the length of exposure time at that particular temperature. However, although the indicator records a time-temperature history, it is not reusable in subsequent applications.
U.S. Pat. No. 3,465,590 (1969) discloses a thermometer device which utilizes solid solutions of fatty acids and a dye to reversibly or irreversibly indicate when a particular temperature has been reached. However, the composition employed in the device does not possess hysteresis behavior thus allowing a predetermined temperature to be observed and recorded. Most importantly, the original temperature-indicating composition cannot be regenerated and is thus not reusable in subsequent applications.